Buccal dosage form

ABSTRACT

A matrix for a buccal dosage form which melts in the oral cavity at body temperature but will not spontaneously deform at higher temperatures encountered in shipment and storage comprises: 
     
         ______________________________________                                    
 
    
     Low MW Polyethylene glycol                                                
                        75-90%                                            
(M.P. about 37° C.)                                                
Medium to high MW polyethylene glycol                                     
                        0-4%                                              
Long chain saturated carboxylic acid                                      
                        0-4%                                              
Polyethylene oxide      0.1-4%                                            
(MW 100,000-5,000,000)                                                    
Colloidal silica         10-20%.                                          
______________________________________

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to dosage forms for buccal administration of medicaments and more particularly to buccal dosage forms providing rapid bioavailability of pharmaceutically active compounds administered by the buccal route.

2. Brief Description of the Prior Art

Administration of pharmaceutical compounds through the buccal mucosa has been found to be an effective means of supplying an effective dose directly to the bloodstream of a patient. The buccal route of administration avoids the possibility that the pharmaceutical compound will be destroyed in the gastrointestinal tract before it can be absorbed, and also eliminates the danger of first-pass inactivation in the liver after absorption. Typically, the buccal dosage form is placed in the buccal cavity between the gum and the cheek, where it dissolves in the patient's saliva, releasing the medicament into the buccal cavity in close proximity to the capillary bed of the oral mucosa. The pharmaceutically active compound then enters the blood in the capillary bed by diffusion through the mucosal tissue and is distributed in the bloodstream to the rest of the body. The rate at which the medication is supplied to the body depends upon, among other things, the rate at which the buccal dosage form dissolves in the mouth. In particular, with patients who have a deficient flow of saliva, a condition found with some frequency in elderly patients and in patients who may be taking medication which tends to depress the flow of saliva, the dosage form may dissolve slowly and supply the medication at a rate which is slower than desired. Such patients also have to endure the discomfort of retaining a foreign object in the buccal cavity, often between the cheek and gum, for a longer period than they might wish.

Hence, a need has continued to exist for a buccal dosage form which will rapidly disintegrate or lose its perceptible shape in the mouth and thereby rapidly and comfortably release its medicament into the buccal cavity independently of the rate of flow of the patient's saliva.

SUMMARY OF THE INVENTION

This need has now been supplied by the buccal dosage form of this invention which provides a rapidly disintegrating buccal dosage form for buccal administration of medicaments, the dosage form comprising a pharmaceutically active compound dispersed in a rapidly dispersing matrix having the following composition, wherein all percentages are by weight:

    ______________________________________                                         Low MW Polyethylene glycol                                                                             75-90%                                                 (M.P. about 37° C.)                                                     Medium to high MW polyethylene glycol                                                                  0-4%                                                   Long chain saturated carboxylic acid                                                                   0-4%                                                   Polyethylene oxide      0.1-4%                                                 (MW 100,000-5,000,000)                                                         Colloidal silica         10-20%.                                               ______________________________________                                    

Accordingly, it is an object of the invention to provide a matrix for a buccal dosage form.

A further object of the invention is to provide rapidly dispersing buccal dosage form.

A further object is to provide a buccal dosage form which disperses rapidly in the buccal cavity at body temperature.

A further object is to provide a buccal dosage form which disperses rapidly in the buccal cavity at body temperature, but retains its shape at elevated temperatures in storage.

Further objects of the invention will become apparent from the description of the invention which follows.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

It has been found desirable in buccal dosage forms which are intended to provide rapid administration of a medicament that the dosage form disperse rapidly in the buccal cavity to provide a fluid which can cover a relatively large area of the oral mucosa. Conventional buccal dosage forms are dispersed by dissolution in the saliva. The dissolution process takes some time, and some individuals, especially elderly patients, may not produce enough saliva to dissolve the dosage form rapidly enough. The dissolution proceeds from the surface of the dosage form while the dosage form retains its general initial shape. The continued presence in the buccal cavity of the undissolved portion of the dosage form may also be annoying to some patients.

The buccal dosage of this invention has been formulated to provide a dosage form which rapidly disperses in the mouth by reason of softening or melting at body temperature to provide a soft gel which can disperse over a large area of the oral mucosa. The ingredients of the dosage form are also, for the most part, water soluble, so that to the extent possible, the matrix of the dosage form will dissolve in the saliva. Because the dosage form melts or greatly softens when placed in the mouth, the surface area of the matrix available to contact the oral mucosa is also increased, and this assists the absorption of the pharmaceutical ingredient of the dosage form through the oral mucosa. Furthermore, the almost immediate melting of the dosage form avoids the discomfort experienced by some patients because of the continued presence of a perceived foreign body in the buccal cavity.

A principal ingredient of the dosage form of the invention is a polyethylene glycol (PEG) having a melting point near 37° C., i.e., near body temperature. Polyethylene glycols having molecular weights in the neighborhood of 1000 are found to have melting points near 37° C. The exact melting point can be adjusted by minor admixtures of PEG's having other molecular weights, as discussed more fully below. When the dosage form comprised largely of the PEG matrix is placed in the patients mouth, it is rapidly warmed to its melting point and rapidly melts and disintegrates within the buccal cavity, thereby carrying the medication into contact with the oral mucosa over a relatively large area. Typically 75-90% by weight of the dosage form is a PEG having a molecular weight of about 1000. Preferably, the amount of PEG 1000 is about 82.5%.

However, a dosage form which melts at the relatively low temperature of 37° C. is in danger of melting and being unacceptably deformed during shipping and storage where it may be exposed to temperatures higher than 37° C. This problem is overcome in the dosage form of this invention by incorporating an amount of colloidal silica along with an amount of polyethylene oxide (PEO) having a molecular weight of 100,000 to 5,000,000. This combination stabilizes the shape of the dosage form when it is exposed to temperatures above 37° C. The colloidal silica and PEO form a dimensionally stable gel when dispersed in the molten PEG. The gel is transparent above the melting point of the ingredients, but retains its shape sufficiently to withstand deformation by the usual handling when individually packaged in a suitable container. When the gel is cooled to a temperature below the melting point of the ingredients, it again becomes hard and generally opaque. To accomplish this purpose, the amount of colloidal silica ingredient is from about 10% to about 20% by weight, preferably from about 12% to about 18% by weight and most preferably about 16% by weight of the composition. The amount of PEO ingredient is about 0.1% to about 4% by weight. Preferably PEO having a molecular weight of about 5,000,000 is present in a proportion of about 0.5% by weight.

Other ingredients are added to the composition of the dosage form of the invention to provide particular properties.

A small proportion of a higher molecular weight PEG may be included to provide precise control over the melting point of the lower molecular weight PEG. PEG's having a molecular weight in the range of 3350-8000 are suitable for this purpose. Higher molecular weight PEG's would also be suitable, provided they have the necessary approval of the Food and Drug Administration for use in pharmaceuticals. PEG 8000 is a preferred high molecular weight PEG. The proportion may vary from 0-4% by weight. Typically, about 0.5% by weight of PEG 8000 is included to adjust the melting point.

In order to reduce the hygroscopicity of the dosage form, a small amount of a long chain carboxylic acid is preferably included. The carboxylic acid may have a carbon chain of 12-18 carbon atoms and is preferably a straight chain saturated aliphatic carboxylic acid. Myristic acid is a preferred long chain carboxylic acid. The proportion of long chain carboxylic acid may vary from 0-4% by weight. The preferred amount of long chain carboxylic acid is about 0.5% by weight.

The dosage form of the invention also incorporates a small amount of a polyethylene oxide (PEO) having a molecular weight of 100,000 to 5,000,000. The high molecular weight polyethylene oxide contributes strength to the molded dosage form and reduces brittleness. It also improves the ability of the dosage form to be prepared by injection molding. The proportion of PEO may vary from 0.1% to about 4% by weight. Preferably PEO having a molecular weight of about 5,000,000 is present in a proportion of about 0.5% by weight.

A preferred composition of the matrix of this invention comprises the following ingredients, wherein the percentages are by weight:

    ______________________________________                                         Polyethylene glycol (MW 1,000)                                                                       82.5%                                                    Polyethylene glycol (MW 8,000)                                                                       0.5%                                                     Myristic acid         0.5%                                                     Polyethylene oxide    0.5%                                                     Colloidal silica      16.0%                                                    ______________________________________                                    

Any conventional pharmaceutical compound suitable for administration by absorption through the buccal mucosa can be incorporated into the dosage form of the invention. Such medicaments include estradiol, synthetic estrogens and progestins, nicotine, prochlorperazine, vitamin B₁₂, ergotamine tartrate, scopolamine, nitroglycerine, buprenorphine, epinephrine, methyltestosterone, triazolam, lidocaine, dronabinol, nabilone and the like.

The invention will be further illustrated by the following examples which are intended to illustrate the practice of the invention and are not to be construed as implying any limitation on the scope of the invention which is defined only by the appended claims.

EXAMPLE 1

This example illustrates the preparation of placebo buccal dosage forms of the invention for use in comparative experiments.

Placebo buccal tablets were prepared in the following manner. A total of 330 grams of polyethylene glycol (MW 1000) was melted and maintained at approximately 75° C. To this was added 2 grams of polyethylene glycol (MW 8000) and 2 grams of myristic acid. The mixture was stirred for approximately 5 minutes Thereupon, 2 grams of polyethylene oxide (MW 5,000,000) was slowly added and mixed for approximately 45 minutes to effect dissolution. Next was added 64 grams of colloidal silica, and the mixture was blended until smooth and homogeneous. The matrix thus prepared was spread in a thin layer and allowed to solidify at room temperature. A portion of the hardened matrix was granulated and fed into an injection molding machine. By this process placebo buccal tablets were prepared having a thin elongated oval shape.

EXAMPLE 2

This example illustrates the preparation of a buccal dosage form of this invention.

Buccal tablets containing methyltestosterone were prepared by a procedure similar to that of Example 1. Each injection molded buccal tablet ha the following composition:

    ______________________________________                                         Ingredient           Amount (mg)                                               ______________________________________                                         Polyethylene glycol (MW 1,000)                                                                      31.25                                                     Polyethylene glycol (MW 8,000)                                                                      0.25                                                      Myristic acid        0.25                                                      Polyethylene oxide   0.25                                                      Methyltestosterone   10.0                                                      Colloidal silica     8.0                                                       ______________________________________                                    

EXAMPLE 3

This example compares the rate of dissolution of the buccal dosage form of this invention with that of a commercial buccal tablet.

The buccal methyltestosterone tablet of Example 2 was compared with a commercial buccal methyltestosterone product containing the same quantity of drug. The test was designed to examine how fast each buccal tablet disappeared in the buccal cavity. Six male volunteers placed a buccal methyltestosterone tablet of Example 2 in the lower frontal buccal space on one side of the mouth and the prior art commercial buccal methyl testosterone product at a comparable location on the opposite side of the mouth. The tablets were located inside the lower lip but outside the tooth line. At various times thereafter, the lower lip was pulled forward and a monitor inspected buccal space visually for disappearance of the buccal tablet. By this procedure the time to dissolve was evaluated for each buccal tablet in each volunteer. The results are shown in Table 1.

                  TABLE 1                                                          ______________________________________                                                 Time to Disappearance (minutes)                                                  Prior Art Commercial                                                                          Buccal Tablet                                         Subject   Buccal Tablet  of Example 2                                          ______________________________________                                         1         >60            12                                                    2         45             6                                                     3         45             3                                                     4         33             6                                                     5         >60            3                                                     6         >60            9                                                     Mean      >50.5          6.5                                                   ______________________________________                                    

These data show that the buccal methyltestosterone tablet of Example 2 disappears much faster than the prior art commercial buccal methyltestosterone product. Additionally, comparisons between the buccal placebo tablets of Example 1 and prior art buccal placebo tablets under development at another laboratory revealed that the buccal placebo tablet of Example 1 disappeared much faster than the prior art developmental tablet. Collectively, these studies establish that the buccal tablets of the present invention are rapid, in comparison to prior art buccal tablets, in disappearance from the buccal cavity.

EXAMPLE 4

This example illustrates preparation of buccal tablets of the invention containing estradiol as the active ingredient.

Buccal tablets containing estradiol were prepared by a procedure similar to that of Example 1. Each oval-shaped buccal tablet had dimensions of 1.0 millimeters by 5.0 millimeters by 10.0 millimeters, weighed 54 milligrams, and contained 0.2 milligrams of estradiol. In preparing the matrix, the drug was added just prior to addition of the colloidal silica. The formulation, stated in the order in which components were added, is as follows:

    ______________________________________                                                               Percent                                                  Ingredient            by weight                                                ______________________________________                                         Polyethylene glycol (MW 1000)                                                                        82.13                                                    Polyethylene glycol (MW 8000)                                                                        0.50                                                     Myristic acid         0.50                                                     Polyethylene oxide (MW 5,000,000)                                                                    0.50                                                     17-beta-estradiol U.S.P                                                                              0.37                                                     Colloidal silica      16.00                                                    ______________________________________                                    

EXAMPLE 5

This example illustrates the rapid achievement of therapeutic blood levels using the buccal tablets of the invention.

A bioavailability study was carried out using the estradiol buccal tablets of Example 4. Six postmenopausal women volunteers took part in the trial. For each volunteer, an estradiol buccal tablet was placed in the buccal cavity at time zero. At appropriate time intervals thereafter, blood samples were drawn and subsequently analyzed for serum estradiol concentration. Table 2 gives values for the time to reach maximum estradiol levels (T_(max)) and the maximum estradiol concentration reached (C_(max)) for each of the six subjects.

                  TABLE 2                                                          ______________________________________                                         Subject     T.sub.max (hours)                                                                         C.sub.max (picograms/ml)                                ______________________________________                                         1           0.5        1180                                                    2           0.75       884                                                     3           0.5        1248                                                    4           1.0        925                                                     5           1.0        817                                                     6           0.5        829                                                     Mean        0.71       980                                                     ______________________________________                                    

These results show that estradiol is rapidly and efficiently absorbed into the blood stream by administration of the estradiol buccal tablets of this invention.

EXAMPLE 6

This example illustrates the preparation of buccal tablets containing nicotine as the active ingredient.

Buccal tablets containing nicotine, to be used as an aid in smoking cessation programs, were prepared as follows. A total of 82 grams of polyethylene glycol (MW 1000) was melted and maintained at 75° C. To this was added 0.5 gram of polyethylene glycol (MW 8000), 0.5 gram of myristic acid, 1.0 gram of citric acid, and 0.5 gram of polyethylene oxide (MW 5,000,000). After dissolution was complete the mixture was cooled to 60° C. Next, 1.0 gram of nicotine was blended into 2.0 grams of colloidal silica, and the blend was added slowly to the other ingredients. Finally, an additional quantity of 12.5 grams of colloidal silica was added and mixing was continued until the molten composition was smooth and homogeneous. The matrix was cooled, granulated, and injection molded to form dosage units weighing 50 milligrams and containing 0.5 milligram of nicotine.

EXAMPLE 7

This example illustrates the administration of nicotine using the buccal tablets of this invention.

Six volunteers, including smokers and non-smokers, placed a nicotine buccal tablet of Example 6 in his or her buccal cavity. Each reported that, within 2 to 5 minutes, physiological effects were felt similar to those experienced or known to exist when smoking cigarettes, i.e., light headedness, tachycardia, and tingling sensations in peripheral extremities. These results indicate that nicotine is rapidly absorbed by administration of nicotine buccal tablets of the present invention.

EXAMPLE 8

This example illustrates the preparation of comparative buccal tablets lacking the colloidal silica ingredient.

Placebo buccal tablets lacking colloidal silica were prepared by a procedure similar to that of Example 1. The composition of these tablets was a follows:

    ______________________________________                                                               Percent                                                  Ingredient            by weight                                                ______________________________________                                         Polyethylene glycol (MW 1000)                                                                        98.5                                                     Polyethylene glycol (MW 8000)                                                                        0.5                                                      Myristic acid         0.5                                                      Polyethylene oxide (MW 5,000,000)                                                                    0.5                                                      ______________________________________                                    

EXAMPLE 9

This example illustrates the shape-retaining properties of the buccal tablets of this invention at elevated temperatures.

Injection molded placebo tablets of Example 8 were compared with those of Example 1 in the following manner. Tablets of Example 8 and tablets of Example 1 having identical size and shape were placed on a flat surface and the test assembly was placed in an incubator at 40° C. Within a few minutes the tablets of Example 8, devoid of colloidal silica, had melted, flattened out on the surface, and had lost all resemblance to their original shape. The tablets of Example 1, however, became optically clear at 40° C. but retained their original shape and were not deformed by gravity. Fine structural details, such as ejector pin marks from the injection molding machine, were retained at 40° C., even though the tablets were a soft gel and could be easily mashed. When the tablets of Example 1 were allowed to cool to room temperature, they became hard again and were virtually identical to tablets not exposed to high temperature. These experiments were repeated at higher temperatures and for longer heating times. In one experiment, tablets of Example 1 kept at 45° C. for 48 hours retained their original shape. These results prove that colloidal silica is an essential ingredient to provide a buccal tablet that has shape retention in the molten state. This property is of considerable value, providing a buccal tablet that can be individually blister packaged and maintain its integrity under adverse thermal exposure during shipping and storage.

EXAMPLE 10

This example illustrates the preparation of buccal tablets lacking the polyethylene oxide ingredient of the tablets of the invention.

Placebo buccal tablets lacking polyethylene oxide were prepared by a procedure similar to that of Example 1. The composition of the matrix was as follows:

    ______________________________________                                                              Percent                                                   Ingredient           by weight                                                 ______________________________________                                         Polyethylene glycol (MW 1000)                                                                       83.0                                                      Polyethylene glycol (MW 8000)                                                                       0.5                                                       Myristic acid        0.5                                                       Colloidal silica     16.00                                                     ______________________________________                                    

EXAMPLE 11

This example compares the tablets of the invention with similar tablets lacking the polyethylene oxide ingredient.

Injection molded placebo tablets of Example 10 were compared with those of Example 1 for their shape retention properties in the molten state. It was observed that tablets of Example 10 did not retain their shape at 40° C. or 45° C. in the same manner as tablets of Example 1, although the difference was not as great as for those lacking colloidal silica (tablets of Example 8). These results, along with those of Example 9, show that both polyethylene oxide and colloidal silica are essential for optimal shape retention in the molten state.

EXAMPLE 12

This example illustrates the preparation of buccal tablets lacking the myristic acid ingredient of the buccal tablets of this invention.

Placebo buccal tablets lacking myristic acid were prepared by a procedure similar to that of Example 1. The composition of these tablets was as follows:

    ______________________________________                                                               Percent                                                  Ingredient            by weight                                                ______________________________________                                         Polyethylene glycol (MW 1000)                                                                        83.0                                                     Polyethylene glycol (MW 8000)                                                                        0.5                                                      Polyethylene oxide (MW 5,000,000)                                                                     0.50                                                    Colloidal silica      16.00                                                    ______________________________________                                    

EXAMPLE 13

This example illustrates the comparative humidity absorption of dosage forms of the invention compared with those which are devoid of myristic acid.

Injection molded placebo tablets of Example 12 were compared with those of Example 1 in the following manner. Tablets of Example 12 and those of Example 1 were carefully weighed and placed in enclosed chambers of known relative humidity. At appropriate times thereafter the samples were removed briefly and weighed to provide a measure of moisture uptake. These data are given in Table 3 and Table 4 for relative humidities of 42% and 79% respectively.

                  TABLE 3                                                          ______________________________________                                         Moisture Uptake at 42% Relative Humidity                                                    Weight increase (percent)                                                        Tablets of                                                                               Tablets of                                            Time (hours)   Example 1 Example 13                                            ______________________________________                                         0.5            0.43      0.59                                                  1              0.76      0.88                                                  2              0.88      1.51                                                  3              1.17      1.53                                                  4              1.38      2.07                                                  24             2.14      2.48                                                  ______________________________________                                    

                  TABLE 4                                                          ______________________________________                                         Moisture Uptake at 79% Relative Humidity                                                    Weight increase (percent)                                                        Tablets of                                                                               Tablets of                                            Time (hours)   Example 1 Example 13                                            ______________________________________                                         0.5            0.82      1.37                                                  1              1.41      2.19                                                  2              2.34      3.79                                                  3              3.28      4.91                                                  4              4.10      6.27                                                  24             17.52     19.32                                                 ______________________________________                                    

These results show that the inclusion of myristic acid in the buccal tablet formulation of this invention results in a less hygroscopic product. This property is of value in the manufacturing and packaging of buccal tablets of the present invention.

EXAMPLE 14

This example illustrates the preparation of buccal tablets with and without the inclusion of polyethylene glycol of molecular weight 8,000.

Placebo buccal matrices lacking polyethylene glycol (MW 8,000) and containing 2% polyethylene glycol (MW 8,000) were prepared by a procedure similar to that used in preparing the matrix of Example 1. The compositions of these two matrices are as follows:

    ______________________________________                                                            Percent (by weight)                                         Ingredient           Matrix A Matrix B                                         ______________________________________                                         Polyethylene glycol (MW 1000)                                                                       83       81                                               Polyethylene glycol (MW 8000)                                                                       0        2                                                Myristic acid        0.5      0.5                                              Polyethylene oxide (MW 5,000,000)                                                                   0.5      0.5                                              Colloidal silica     16       16                                               ______________________________________                                    

EXAMPLE 15

This example illustrates the comparative melting points of the compositions prepared in Example 14.

The melting points were determined for the matrices of Example 14 and the matrix of Example 1. The results are shown in Table 5.

                  TABLE 5                                                          ______________________________________                                                     PEG (MW 8,000)                                                                              Melting range                                         Matrix      (percent)    (°C.)                                          ______________________________________                                         Example 14A 0            35.5-36.0                                             Example 1   0.5          36.0-36.5                                             Example 14B 2.0          38.5-39.0                                             ______________________________________                                    

These results show that small quantities of polyethylene glycol (MW 8,000) can be used to regulate the melting point of the buccal matrix in the range of body temperature.

The invention having now been fully described, it should be understood that it may be embodied in other specific forms or variations without departing from its spirit or essential characteristics. Accordingly, the embodiments described above are to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein. 

I claim:
 1. A matrix composition for a buccal dosage form comprising

    ______________________________________                                         Low MW Polyethylene glycol                                                                           70-90%   by weight                                       having a molecular weight                                                      of about 1000                                                                  (M.P. about 37° C.)                                                     Medium to high MW Polyethylene glycol                                                                0-4%     by weight                                       having a molecular weight                                                      of about 3350 to about 8000                                                    Long chain saturated carboxylic acid                                                                 0-4%     by weight                                       Polyethylene oxide    0.1-4%   by weight                                       (MW 100,000-5,000,000)                                                         Colloidal silica      10-20%   by weight                                       ______________________________________                                    


2. The composition of claim 1 wherein said low MW polyethylene glycol is PEG
 1000. 3. The composition of claim 1 wherein said medium to high MW polyethylene glycol is PEG
 8000. 4. The composition of claim 1 wherein said long chain saturated carboxylic acid has 12 to 18 carbon atoms in the chain.
 5. The composition of claim 3 wherein said long chain carboxylic acid is myristic acid.
 6. The composition of claim 1 wherein said polyethylene oxide has a MW of about 5,000,000.
 7. The composition of claim 1 wherein said low molecular weight polyethylene glycol is present in a proportion of about 82.5% by weight.
 8. The composition of claim 7 wherein said low molecular weight polyethylene glycol is PEG
 1000. 9. The composition of claim 1 wherein said medium to high molecular weight PEG is present in a proportion of about 0.5% by weight.
 10. The composition of claim 9 wherein said medium to high molecular weight PEG is PEG
 8000. 11. The composition of claim 1 wherein said long chain saturated carboxylic acid is present in a proportion of about 0.5% by weight.
 12. The composition of claim 11 wherein said long chain saturated carboxylic acid has 12 to 18 carbon atoms in the chain.
 13. The composition of claim 12 wherein said long chain carboxylic acid is myristic acid.
 14. The composition of claim 1 wherein said polyethylene oxide is present in a proportion of about 0.5% by weight.
 15. The composition of claim 1 wherein said polyethylene oxide has a molecular weight of about 5,000,000.
 16. The composition of claim 15 wherein said colloidal silica is present in a proportion of about 12% to about 18% by weight.
 17. The composition of claim 16 wherein said colloidal silica is present in a proportion of about 16% by weight.
 18. A matrix composition for a buccal dosage form comprising

    ______________________________________                                         Polyethylene glycol (MW 1000)                                                                        82.5% by weight                                          Polyethylene glycol (MW 8,000)                                                                        0.5% by weight                                          Myristic acid          0.5% by weight                                          Polyethylene oxide     0.5% by weight                                          Colloidal silica      16.0% by weight                                          ______________________________________                                     